1. Field of the Invention
The present invention relates to a heat treatment method and a heat treatment apparatus, and more particularly to a technique for performing a heat treatment on an increased number of substrates with uniformity of the treatment ensured.
2. Description of the Related Art
In the process for manufacturing semiconductor devices, various treatment apparatuses (semiconductor manufacturing apparatuses) are used to perform treatments such as oxidization, diffusion, and chemical vapor deposition (CVD) on substrates to be treated, e.g., semiconductor wafers (hereinafter also referred to as wafers). As one of the treatment apparatuses, a heat treatment apparatus is known, which is capable of performing a heat treatment on multiple substrates simultaneously.
The abovementioned heat treatment apparatus has a heat treating furnace and a boat. The boat is a substrate holder, which holds multiple wafers at a predetermined vertical interval and is carried into and out of the heat treating furnace (refer to JP-A-2001-223254). In addition, the heat treatment apparatus includes an elevation mechanism and a transfer mechanism. The elevation mechanism and the transfer mechanism are located in a loading area (operation area) present under the heat treating furnace. The elevation mechanism is operable to lift and lower a lid under the condition that the boat is placed on a thermal insulation tube (that is furnace throat heat insulating means) present on the lid for closing the furnace throat in order that the boat is carried into the heat treating furnace from the loading area and carried out of the heat treating furnace into the loading area. The transfer mechanism is operable to transfer wafers between the boat carried into the loading area and a container capable of accommodating the wafers.
The boat has a plurality of columns between a bottom plate and a top plate. Each of the columns has substrate holding sections arranged at a predetermined vertical interval (pitch). The substrate holding sections are grooves or protrusions for holding edge portions of the wafers. All the wafers are held by the boat under the condition that front surfaces (to be treated) of the wafers face upward.
However, the minimum pitch of the substrate holding sections, which depends on the number of wafers to be held by the boat, is determined based on uniformity of the surface (to be treated) of each of the wafers, uniformity between the surfaces (to be treated) of the wafers and the number of the wafers to be placed. It is, therefore, difficult to increase the number of wafers to be held by the boat. If the pitch is increased to improve the uniformity of the surface of each of the wafers and the uniformity between the surfaces of the wafers, the number of the wafers is reduced.